process for the production of mixtures of 2, 5 - dimethylpyrazin and cis - and trans - 2, 5 - dimethylpiperazin

摘要

The Specification claims the processes of (1) isomerizing cis - or trans - 2:5 - dimethylpiperazine to produce a mixture of the two by heating with a nickel-containing hydrogenation-dehydrogenation catalyst in an atmosphere of hydrogen (preferably under pressure); and (2) producing a mixture of at least 50 per cent of trans-2:5-dimethylpiperazine with some cis-2:5-dimethylpiperazine and 2:5-dimethylpyrazine by heating isopropanolamine to 180-260 DEG C. under hydrogen pressure of at least 200 p.s.i. for at least 2 hours in the presence of a nickel hydrogenation-dehydrogenation catalyst. The equilibrium mixture obtained under these conditions contains about 80 per cent of the trans-compound so that process (1) can be used to enrich the trans-form if it is present initially to the extent of less than 80 per cent or to enrich the cis-form if less than 10 per cent thereof is present. Similarly the amount of trans-compound resulting from process (2) can be increased by adding the cis-form to the isopropanolamine. Preferred conditions for process (2) are a temperature of 200-240 DEG C. (e.g. 220-240 DEG C.), hydrogen pressure of 800-1200 p.s.i., 4 hours or more of heating, and 1.25 g. or more (e.g. 2.5 g.) of an alloy sketal catalyst of the Raney nickel type. Information is given as to the variation of yield and conversion under different experimental conditions. The filtered reaction product is heated to distil off water and 2:5-dimethylpyrazine, and unreacted isopropanolamine removed as an azeotrope with ethylbenzene or xylene; these products can be recycled. The cis- and trans-2:5-dimethylpiperazines may be partially separated by fraction distillation, the trans-form being purified by crystallization from a melt and the cis-form by solution in heptane. This separation can be carried out continuously or batchwise, suitable plant for the former being illustrated. Specification 791,050 is referred to.